Role of Microstructure and Doping on the Mechanical Strength and Toughness of Polysilicon Thin Films

PROJECT TITLE :

Role of Microstructure and Doping on the Mechanical Strength and Toughness of Polysilicon Thin Films

ABSTRACT:

The role of microstructure and doping on the mechanical strength of microscale tension specimens of columnar grain and laminated polysilicon doped with completely different concentrations of phosphorus was investigated. The typical tensile strengths of undoped columnar and laminated polysilicon specimens were one.three ± 0.1 and a couple of.45 ± 0.3 GPa, respectively. Heavy doping reduced the strength of columnar polysilicon specimens to 0.9 ± zero.1 GPa. On grounds of Weibull statistics, the experimental results from specimens with gauge sections of a thousand μm × 100 μm × one μm predicted quite well the tensile strength of specimens with gauge sections of 150 μm × 3.seventy five μm × one μm, and vice versa. The massive distinction in the mechanical strength between columnar and laminated polysilicon specimens was due to sidewall flaws in columnar polysilicon, which were introduced throughout reactive ion etching (RIE) and were additional exacerbated by phosphorus doping. Removal of the massive defect regions at the sidewalls of columnar polysilicon specimens via ion milling increased their tensile strength by seventyp.c-a hundred%, approaching the strength of laminated polysilicon, which implies that the 2 types of polysilicon films have comparable tensile strength. Measurements of the effective mode I essential stress intensity issue, KIC,eff, also showed that each one sorts of polysilicon films had comparable resistance to fracture. Therefore, further processing steps to eliminate the sting flaws in RIE patterned devices might result in significantly stronger microelectromechanical system parts fabricated by typical columnar polysilicon films.

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